1. Field of the Invention
The present invention relates to a serial-to-parallel conversion (SPC) circuit for converting the serial digital data into the parallel digital data. It also relates to a semiconductor device including the SPC circuit.
2. Description of the Related Art
An example of a semiconductor device whose input signals are digital data, is a liquid crystal display device of active matrix type. In recent years, the active matrix type liquid crystal display device has come to be constructed of a plurality of TFTs (thin film transistors) formed from polycrystalline silicon, and to be unitarily formed with an active matrix circuit for displaying an image and driver circuits for driving the active matrix circuit.
A serial-to-parallel conversion (SPC) circuit for digital data receives the inputs of digital data (hereinbelow, termed xe2x80x9cinput digital dataxe2x80x9d) as the input signals, and feeds the source signal line driver circuit of the active matrix type liquid crystal display device with digital data modified by temporally expanding the pulse length of the input digital data (the pulse length may be expanded any times, but it is most commonly expanded n times where letter n denotes a natural number of at least 2). The temporal expansion of the pulse length of the input digital data to n times is nothing but lowering the frequency of the input digital data to 1/n.
The SPC circuit for digital data has significance as stated below. The digital data to be inputted to the active matrix type liquid crystal display device are ordinarily at several tens MHz, but the digital data at one hundred and several tens MHz might be generalized in compliance with recent requirements for a higher definition, a higher resolution and more gradations.
Nevertheless, the TFTs included in the source signal line driver circuit of the active matrix type liquid crystal display device have had performances insufficient for processing the digital data of such a higher frequency, and they have been incapable of operating or have had difficulty in reliability. It is accordingly indispensable to lower the frequency of the input digital signals down to the degree at which the source signal line driver circuit is capable of operating to perfection. In this regard, the SPC circuit for digital data functions to lower the frequency of the input digital data. Incidentally, the scale of the SPC circuit for digital data is smaller as compared with that of the source signal line driver circuit, and a clock signal within the SPC circuit is less liable to become xe2x80x9cdullxe2x80x9d (as a signal delay at the rise or fall of the pulse of the clock signal), so that the SPC circuit can be driven at a higher speed.
As stated above, the SPC circuit for digital data can be driven faster than the source signal line driver circuit etc. The faster operation of the SPC circuit, however, has been somewhat objectionable in the points of reliability and stability in complying with the recent requirements for a higher definition, a higher resolution and more gradations.
An example of the SPC circuit for digital data having hitherto been used by the inventors is an SPC circuit for digital data disclosed in Japanese Patent Application Laid-open No. 11-231798 (1999), assigned to the same assignee as that of the present application. The Japanese Patent Application corresponds to a U.S. patent application Ser. No. 09/206,297 and a European Patent Application Laid-open No. 0 921 517 A.
The exemplified SPC circuit for digital data necessitates for its operation a clock signal at the same frequency as that of the input digital data. By way of example, in order to convert the serially inputted digital data of 80 MHz into eight parallel digital data, the SPC circuit is normally fed with the clock signal of 80 MHz. The operation has been problematic in power dissipation, stability, reliability, etc.
The present invention has been made in view of the above problems, and has for its object to provide a novel serial-to-parallel conversion (SPC) circuit for digital data that is excellent in power dissipation, stability and reliability.
The constructions of an SPC circuit and a semiconductor display device including the SPC circuit, according to the present invention, will be summarized below.
According to the present invention; a serial-to-parallel conversion (SPC) circuit for digital data converts the digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letter y denotes a natural number), the serial-to-parallel conversion circuit for digital data operates with a plurality of clock signals of, at the highest, (m/2) Hz.
In this manner, the SPC circuit of the present invention is permitted to operate with the clock signals at frequencies of, at the highest, xc2xd of the frequency of the digital data to-be-inputted.
By the way, in this specification, the frequencies of clock signals and digital signals will be often stipulated, but they shall be rough frequencies that cover equivalent frequencies.
Also, according to the present invention; a serial-to-parallel conversion (SPC) circuit for digital data converts the digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letter y denotes a natural number), the serial-to-parallel conversion circuit for digital data operates with a plurality of clock signals of, at the highest, (m/2) Hz and at the lowest, (mxc2x72xe2x88x92y) Hz.
Besides, according to the present invention: a serial-to-parallel conversion (SPC) circuit for digital data converts digital data of respective bits of the x-bit digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letters x and y denote natural numbers); the serial-to-parallel conversion circuit for digital data comprises x SPC/bit circuits to which the digital data of the respective bits of said x-bit digital data are inputted, each of said SPC/bit circuits includes first stage through y-th stage circuits, the y-th stage circuit lowers the frequency of 2yxe2x88x921 digital data inputted serially to xc2xd and converts the 2yxe2x88x921 digital data into the 2y parallel digital data.
In addition, according to the present invention: a serial-to-parallel conversion (SPC) circuit for digital data converts digital data of respective bits of the x-bit digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letters x and y denote natural numbers); the serial-to-parallel conversion circuit for digital data comprises x SPC/bit circuits to which the digital data of the respective bits of said x-bit digital data are inputted, each of said SPC/bit circuits includes basic units in a number indicated by Formula (1) given below, each of said basic units in the number indicated by Formula (1) lowers a frequency of digital data inputted serially to xc2xd and converts the digital data inputted serially into two parallel digital data.                               ∑                      k            =            1                    Y                ⁢                  2                      k            -            1                                              (        1        )            
Yet in addition, according to the present invention: a semiconductor display device having an active matrix circuit in which pixel TFTs are arranged in a matrix shape, a source signal line driver circuit and a gate signal line driver circuit which drive the active matrix circuit, and a serial-to-parallel conversion circuit for digital data which converts the digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letter y denotes a natural number); the semiconductor display device operates with a plurality of clock signals of, at the highest, (m/2) Hz.
Further, according to the present invention: a semiconductor display device having an active matrix circuit in which pixel TFTs are arranged in a matrix shape, a source signal line driver circuit and a gate signal line driver circuit which drive the active matrix circuit, and a serial-to-parallel conversion circuit for digital data which converts the digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letter y denotes a natural number); the semiconductor display device operates with a plurality of clock signals of, at the highest, (m/2) Hz and at the lowest, (mxc2x72xe2x88x92y) Hz.
Still further, according to the present invention: a semiconductor display device having an active matrix circuit in which pixel TFTs are arranged in a matrix shape, a source signal line driver circuit and a gate signal line driver circuit which drive the active matrix circuit, and a serial-to-parallel conversion circuit for digital data which converts digital data of respective bits of the x-bit digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the parallel digital data (where letter m denotes a positive number, and letter y denotes a natural number); the serial-to-parallel conversion circuit for digital data includes x SPC/bit circuits to which the digital data of the respective bits of said x-bit digital data are inputted, each of said SPC/bit circuits includes first stage through y-th stage circuits, the y-th stage circuit lowers a frequency of the 2yxe2x88x921 digital data inputted serially to xc2xd and converts the 2yxe2x88x921 digital data into the 2y parallel digital data.
Yet further, according to the present invention: a semiconductor display device having an active matrix circuit in which pixel TFTs are arranged in a matrix shape, a source signal line driver circuit and a gate signal line driver circuit which drive the active matrix circuit, and a serial-to-parallel conversion circuit for digital data which converts digital data of respective bits of the x-bit digital data inputted serially at m Hz into 2y parallel digital data of (mxc2x72xe2x88x92y) Hz and outputs the 2y parallel digital data (where letter m denotes a positive number, and letters x and y denote natural numbers); the serial-to-parallel conversion circuit for digital data includes x SPC/bit circuits to which the digital data of the respective bits of said x-bit digital data are inputted, each of said SPC/bit circuits includes basic units in a number indicated by Formula (1) given below, each of said basic units in the number indicated by Formula (1) lowers a frequency of digital data inputted serially to xc2xd and converts the digital data inputted serially into two parallel digital data.                               ∑                      k            =            1                    y                ⁢                  2                      k            -            1                                              (        1        )            